1. Field of the Invention
The invention relates to a shock-absorbing system for footwear, particularly sports footwear, such as walking shoes, running shoes, and the like. More particularly, the invention relates to an article of footwear having such system, such system comprising a shock-absorbing bottom assembly.
2. Description of Background and Relevant Information
There are a large number of shock-absorbing, or damping, systems for sports footwear, which are adapted to damp the reactive forces coming from the ground during the course of walking or running, or during other movement.
These damping devices are conventionally designed for damping the reactive forces that occur mainly perpendicular with respect to the surface of the ground, that is, primarily vertically directed forces. Indeed, the reactive forces occurring in this direction are conventionally considered as being the most substantial. Therefore, these vertical reactive forces are generally damped by merely providing a foam block generally made of EVA and which is vertically deformable. Other means using pockets filled with fluid or gas are also known.
Focus has been directed more recently to those ground reactive forces that occur in the plane of the ground, rather than vertically, which will be referred to hereinafter as the horizontal plane.
Depending upon the type of sport practiced, such horizontal forces are more or less substantial. For example, in sports such as tennis or basketball, where a number of movements are lateral, the reactive forces occurring along the ground plane can be very high.
The horizontal reactive forces that occur when running on asphalt are higher, because the high coefficient of friction of asphalt stops any relative horizontal movement of the sole with respect to the ground, which is not the case when running on looser ground, on which ground/sole relative movements can occur.
This finding has led to new footwear constructions, in which the sole damping devices are designed so as to permit a certain relative movement of the sole with respect to the ground, and/or shearing movements within the sole itself, in order to absorb the forces occurring in an essentially horizontal plane and to reproduce the effects of running on loose ground.
Such constructions are known, for example, from the documents U.S. Pat. Nos. 6,487,796, 5,343,639, 6,962,008, EP 1 402 795, and U.S. Pat. No. 5,224,810.
These documents generally teach damping only in the horizontal plane.
The documents WO 98/07343 and U.S. Pat. No. 6,266,897 disclose a construction in which pocket-like elements filled with fluid can deform in all three directions, that is, in the horizontal plane as well as in the vertical direction.
The drawback of such a construction is that deformations in any of the directions are uniform. Therefore, it is not possible to distinguish/dissociate the vertical damping from the horizontal damping.
Another problem common to all of the damping devices is in reconciling damping and stability of the foot on the ground, such as the “grip” the shoe has relative to the ground, these functions being more or less incompatible.